class Solution4 {
    public int change(int amount, int[] coins) {
          int len = coins.length ;
          int[] dp = new int[amount+1] ; 
          dp[0] = 1 ;
          for(int i=0 ; i< len ; i ++){
            for(int j=1 ;j<=amount ; j++){
                if(j>=coins[i]){
                    dp[j] += dp[j-coins[i]] ; 
                }
            }
          }
        return dp[amount] ;  
    }
}